Turbine engines are used as the primary power source for many types of aircrafts. The engines are also auxiliary power sources that drive air compressors, hydraulic pumps, and industrial gas turbine (IGT) power generation. Further, the power from turbine engines is used for stationary power supplies such as backup electrical generators for hospitals and the like.
Most turbine engines generally follow the same basic power generation procedure. Compressed air generated by axial and/or radial compressors is mixed with fuel and burned, and the expanding hot combustion gases are directed against stationary turbine vanes in the engine. The vanes turn the high velocity gas flow partially sideways to impinge on the turbine blades mounted on a rotatable turbine disk. The force of the impinging gas causes the turbine disk to spin at high speed. Jet propulsion engines use the power created by the rotating turbine disk to draw more air into the engine and the high velocity combustion gas is passed out of the gas turbine aft end to create forward thrust. Other engines use this power to turn one or more propellers, fans, electrical generators, or other devices.
In an attempt to increase the efficiencies and performance of contemporary gas turbine engines generally, engineers have progressively pushed the engine environment to more extreme operating conditions. The harsh operating conditions of high temperature and pressure that are now frequently specified place increased demands on engine component-manufacturing technologies and new materials. Indeed the gradual improvement in engine design has come about in part due to the increased strength and durability of new materials that can withstand the operating conditions present in the modern gas turbine engines. With these changes in engine materials, there has arisen a corresponding need to develop new repair methods appropriate for such materials.
Through normal service, there arises a need to repair engine components such as turbine impellers and blisks. With respect to blisks, blade leading edge damage is one of the most common failures. The leading edge is subject to foreign object damage or erosion after a period of service time. A significant savings can be realized if the damaged blades can be repaired and returned to service.
Historically, the repair has been accomplished by machining away the damaged portion of the blades. Welding material was then manually deposited over the areas that had been machined away. The component was then machined by referencing a nominal model geometry in an attempt to reproduce the originally designed dimensions. Then, the component was hand finished, manually machined, in order to put the component in a serviceable condition.
However, there are shortcomings associated with the historical repair method. The method requires leaving a significant amount of remaining material (stock on) after machining, which must be removed by a hand finishing process. This is due to the fact that no component, or blade within a component, is exactly at a nominal condition. The manual nature of the hand finishing process increases the cost and processing time of the repair. Finally, the method results in significant scrap. Thus, a need exists for the development of improved machining and weld repairing methods.
The option of throwing out worn engine components such as turbine blisks and replacing them with new ones is not an attractive alternative. Blisks are extremely expensive due to their costly material and manufacturing process. Consequently there is a strong financial need to find an acceptable and efficient repair method for engine components.
Hence, there is a need for a repair method that addresses one or more of the above-noted drawbacks and needs. Namely, a repair method is needed that can restore the approximate geometry, dimension and desired properties of degraded gas turbine engine components and/or a method that allows an efficient repair of worn airfoil surfaces and/or a repair method that minimizes the amount of stock on material on a welded piece after machining. Finally, it would be desired to provide a repair method that by virtue of the foregoing is therefore less costly as compared to the alternative of replacing worn parts with new ones. The present invention addresses one or more of these needs.